Voltage-supply means for directional relays



Sept. 13, 1932. R. c. CURTIS 1,877,446

VOLTAGE SUPPLY MEANS FOR DIRECTIONAL RELAYS Filed June 16. 1930 INVENTOR E/c/vam a. cmz

ATT.ORNEY Patented Sept. 13, 1932 UNITED STATES PATENT OFFICE RICHARD C. CURTIS, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA VOLTAGE-SUPPLY means r03 DIRECTIONAL RELAYS Application filed June 16,

My invention relates to relay systems and it has particular relation to such systems utilizing instantaneously operating faultresponsive elements with which are associated instantaneous directional elements which are designed to respond to the direction ofthe line current with respect to a comparisoncorrectly operate.

My invention consis s of the circuits, apparatus and systems hereinafter described and claimed, as shown in the accompanying drawing, wherein Figure 1 is a diagrammatic view of the circuits and apparatus embodying my invention, and

Fig. 2 is an equivalent diagram referred to in the mathematical analysis of my circuit.

My invention is shown as being applied, by way of example, to an electrical system comprising a three-phase transmission line 3 which is connected to a bus 4 through a three-pole circuit breaker 5, the latter hav;

ing a tripping coil 6 which is energized from a battery or other source 7 through contacts 8 on a directional or wattme'ter element 9, and contacts 11 on an impedance element 12, the latter having a current-responsive actuating coil 13 and a voltage-responsive restraining coil 14. The directional element 9 and the impedance element 12 are both instantaneous, the former-operating innot more than about 1' cycle, on a (SO-cycle systern, and the latter operating within about 2 cycles. v p 4 The current winding 13'i0f the impedance element and the current terminals 16 of the directional element are energized in any desired manner from t e line current, as indicated very schematically by a current 1930. Serial no. 461,619.

transformer 17. The voltage coil 14 of the impedance element is also energized from any suitable voltage source which is also indicated very schematically by a potential transformer 18. It will be understood that the mode of energization of the voltage and.

special tuned network 22 which has the effect of holding up the voltage across the terminals 21 for a few cycles after the line voltage has been reduced to zero, as by means of a severe fault nearby. I

The network 22 comprises a parallel-resonant circuit consisting of a condenser or capacitor 24 which is shunted by an inductance coil 25 in series with an auxiliary-cur- 5 transformer 18, as heretofore, but through a rent transformer 26', the secondary Winding of which is connected to a voltage bus 28 for one or more directional delay elements 9. The tuned circuit 24, 25 is energized from the potenti'al transformer 18, or any other potential transformer, through an external resistanceJ30; If desired, an auxiliary loading resistance 32 may be permanently connected across the terminals of the secondary winding of the auxiliary current-transformer 26 in order to limit the rise of voltage on the voltage bus 28 when the voltage terminals of the directional element are disconnected from the bus.

In Fig. 2, an ,equivalentcircuit is shown, in which R, is the total resistance of the tuned circuit, including the inevitable resistance of the reactance coil and the equivalent resistance of the connected relay coils, L is the total inductance of the tuned circuit, being substantially the inductance ofthe reactance coil, C is the capacity of the condenser, R is the resistance of the circuit'external to the tuned circuit, being substantially the resistance of the external resistor, E is E Eleminating 71 from these equations, we obtain a linear diflerential equation in terms of 2' Thus d 1' R (i m itan xii t al 1 E (1 +7? Z7111 R-LCS1D cat,

which integrates to The first term of equation (4) involves the dampening factor, expressing the fraction of the initial relay voltage which will be obtained in a time t after the collapse of the applied voltage E. The second term, or the part in parenthesis, in equation (4) involves .the quantity B, which is 2m times the natural oscillating frequency of the tuned circuit,

and which must be so close to the line frequency, or must be so nearly equal to in), that the oscillating current in the tuned circuit does not get much out of phase with the-corresponding line-frequency current during the operating period of the relay. It is unnecessary, for our present purposes, to determine the integrating constants A and B.

The tuning of the oscillating circuit is very little affected by the resistances R and R, the detuning efiects of which very nearly cancel each other even if their values should change by 5% or more. Thus, remembering that, in any tuned circuit, L0(o ='1, and assuming, as we must, that the resistance R is small compared to the reactance X=wL, say

which is practical in a -cycle circuit, the decrement-constant, or significant factor a in -at, which is the exponent in the first term of equation (4), becomes If we further assume that the external reor R 30X 30wL, the decrement-constant becomes .i 2 e "E RO 'Z '2('3 0 30 30 Turning, now, to the tuning-factor B, of equations (4) and (5), we may write 1w 0.1 1 2 x atafiaol (with Jan am) :j It will be seen that the resistance-effects, as represented by the factors 'directional relay 9, which imposesa definite limit as to the. amount of dephasing which may be tolerated during the switching period. If we assume, for example, that the oscillating circuit must not get out of step more than 0.05 cycle, or 18, at the end of 10' cycles, or 196 in 11 cycles, B must lie within the limits jw(1i.005) and hence the reactances must be tuned so closely that which means fairly close tuning (for a 60- cycle circuit) within 1%, which is entirely feasible. The impedance ZCJLL of the parallel circuits R jQL and This means that half of the voltage E- is con- ,sumed in the external resistance R.

1 It will be understood, of course, that the foregoing calculations are merely illustra-' tive, and that I am not limited altogether to the relative values stated. The ratios R R 1 :X- 30 and 3T) give a decrement, as shown by the first term of equation (4), such that the relay voltage drops to one-tenth of its normal value in 11 kink cycles after the collapse of the line voltage E, or when 1 f .183. Thus, since (0 377 in a 60-cycle system,

Putting 7c=the fraction of the initial voltage lappearing after a given time, as 11 cycles, we

ave

The values of the resistances R and R have a direct influence on the decrement of.

the voltage. In a GO-cycle circuit, we know that we can make the ratio of X to R =30 in a' practical circuit. This ratio may be made as high as 50, with a very costly circuit, but we cannot get much higher. The

relay-coil circuit 21 may have the same ratio,-

and the current transformer 26 will have a neghgible eflect. the fraction which is to be added to I R0 it would not pay to have R much larger than 30X, or to have a much larger denominator i. RO 30 Thus, if the external resistance were three times as large, so that three-quarters of the impressedenergy is consumed in the external resistance R, instead of one-half being consumed therein, the value of the decrementconstant or would decrease only 33%, or to and k=0.2l5, which means that the would reduce to 21-1/2% of its initial value 'in 11 cycles, or to 10% in g 11=16-1/ cycles, or to 1% in 33 cycles. This three-fold increase in the external resistance would change the tuning of ,8 by only 1/160 of one percent, which is well within the required accuracy of 1/2 of one percent A decrease in either ratio Ot I voltage would have a very strong damping effect, quickly renderingthe circuit useless. Thus, with an external resistor a third as large, or R=10X, and the same ratio of reactance to resistance in the tuned circuit, which would change the tuning'to within other limits, as indicated by those of the appended claims which are ited.

I claim as my invention:

1. Voltage-supply means for alternatingcurrent relay-elements comprising a tuned parallel resonant circuit in series with an external impedance having a value suflicient to permit said tuned circuit to oscillate, a relay-voltage bus, and means for applying a voltage from the tuned circuit to said bus, characterized by the fact that the ratio of reactance to resistance in the equivalent cirnot so limc'uit of said tuned circuit is of the order of 30, more or less.

2. Voltage-supply means for alternatingcurrent relay-elements comprising a tuned parallel resonant circuit in series with an external impedance having a value sufiicient to permit said tuned circuit to oscillate, a relayvoltage bus, and means for applying a voltage from the tuned circuit to said bus, characterized by the fact that the ratio of reactance to resistance in the equivalent circuit of said tuned circuit is of the order of 30, more or less, and the ratio of the external impedance tothe combined impedance of the parallel paths of the tuned circuit is of the order of unity, .more or less.

3. Voltage-supply means for alternatingcurrent relay-elements comprising a tuned parallel resonant circuit in series with an ex- 7 ternal impedance having a value sufiicient to permit said tuned circuit to oscillate, a relayvoltage bus, and means for applying a volt- .age from the tuned circuit to said bus, characterized by the fact-that the ratio of the external impedance to the combined impedance of the parallel paths of the tuned circuit is of the order of unity, more or less.

4. Voltage-supply means for alternatingcurrent relay-elements comprising a tuned parallel resonant circuit in series with an .external resistance having a value sufficient to permit said tuned circuit to oscillate, a transof reactance to resistance in the equivalent former in series with the oscillating current in the tuned circuit, and a relay-voltage bus connected to the terminals of said trans former, characterized by the fact that the ratio of reactance to resistance in the equivalent circuit of said tuned circuit is of the order of 30, more or less.

5. Voltage-supplymeans for alternatingcurrent relay-elenients comprising a tuned parallel resonant circuit in series with an external resistance having a value sufiicient to permit said tuned circuit to oscillate, a transformer in series with the oscillating current in the tuned circuit, and a relay-voltage bus connected to the terminals of said transformer, characterized by the fact that the ratio circuit of said tuned circuit is of the order of 30, more or less, and the ratio of the eX- ternal resistance to the combined impedance of the parallel paths of the tuned circuit is of the order of unity, more or less.

6. Voltage-supply means for alternatingcurrent relay-elements comprising a tuned parallel resonant circuit in series with an external resistance having a value sufiicient to permit said tuned circuit to oscillate, a transformer in series with the oscillating current in the tuned circuit, and a relay-voltage bus connected to the terminals of said transformer, characterized by the fact that the ratio of the external resistance to the combined impedance oi' the parallel paths of the tuned circuit is of the order of unity, more or less.

7. Voltage-supply means for alternatingcurrent relay-elements comprising a tuned parallel resonant circuit in series with an external resistance having a. value sufficient to permit said tuned circuit to oscillate, a transformer in series with the oscillating current in the tuned circuit, and a relay-voltage bus connected to the terminals of said trans former, characterized by the fact that the ratio of the external resistance to the equivalent resistance in the tuned circuit is of the order of several hundreds.

8. Voltage-supply means for alternatingcurrent relay-elements comprising a tuned parallel resonant circuit in series with an external resistance having a value suflicient to permit said tuned circuit to oscillate, a. trans formerin serieswith the oscillating current in the tuned circuit, and a relay-voltage bus connected to the terminals of said transformer, characterized by the fact that the ratio of the external resistance to the reactance in the tuned circuit is of the order of 30, more or less.

9. Voltage-supply means for alternatingcurrent relay-elements comprising a tuned parallel resonant circuit in series with an external resistance having a value suilicient to permit said tuned circuit to oscillate, a current transformer in series with the oscillating current in the tuned circuit, and a relayvolta e bus connected to the terminals of said trans ormer, characterized by the fact that a ballast resistance is connected across said relay-voltage bus.

10. A relaying system for a transmission line, characterized by having an instantaneous fault-distance-responsive relay element, and a directional element associated therewith for responding to the direction of the line currents, further characterized by a volt age-supply means for said directional element comprisin a tuned parallel resonant circuit in series with an external impedance having a value sufficient to permit said tuned circuit to oscillate, a transformer in series with the oscillating current in the tuned circuit, and a relay-voltage bus connected to the terminals of said transformer.

11. A relaying system for a transmission line, characterized by a line-sectionalizing switching means and a relaying means therefor, said relaying means having an instantaneoiis fault-distance-responsive relay elecircuit in series with an external resistance,

having a value sufiicientto permit said tuned circuit to oscillate, a directional element relay-voltage bus, and means for applying a voltage from the tuned circuit to said bus.

12. The invention as defined in claim 10 characterized by such ratios of reactance and resistances that the directional-element voltage drops to 10% of its normal value in not more than something of the order of a sixth of a second, more or less, after the complete collapse of the line voltage.

13. The invention as defined in claim 11, characterized by such ratios of reactance and resistances that the directional-element voltage drops to 10% of its normal value in not more than something of the order of a sixth of a second, more or less, after the complete collapse of the line voltage.

14. The invention as defined in claim 10, characterized by such ratios of reactance and resistances that the directional-element voltage drops to 10% of its normal value in something of the order of about 5 to 15 cycles after the complete collapse of the line voltage.

15'. The invention as defined in claim 11 characterized by such ratios-of reactance and resistances that the directional-element voltage drops to 10% of its normal value in something of the order of about 5 to 15 cycles after the complete collapse of the line voltage.

16. The invention as defined in claim 11 characterized by such ratios of reactance and resistances that the directional-element voltage drops to a fraction of its initial normal Value which is above the minimum critical value at which the directional relay will be operative, within a time necessary to eifect the switching operation after the occurrence of a severe fault on the transmission line.

17. The invention as defined in claim 11 characterized by such ratios of reactance and resistances that the directional-element voltage drops to a fraction of its initial normal value which is above the minimum critical value at which the directional relay will be operative, within a time necessary to efiect the switching operation after the occurrence of a severe fault on the transmission line, and further characterized by such accurate tuning that the total aggregate phase-departure of the tuned circuit from the impressed voltage during said time necessary for switching shall not be more than the directional relay will stand Without false operation.

18. A protective relaying system for a transmission line including a directional relay having a voltage winding, a' voltage supply means energized from said line for said voltage winding including a tuned parallel resonant circuit in series with an external impedance having a value sufiicient to permit said tuned circuit to oscillate.

In testimony whereof, I have hereunto subscribed my name this 6th day of June, 1930.

RICHARD C. CURTIS. 

